This invention relates to a process for making steel from iron ore without proceeding through the liquid state.
Presently, steel is produced in five basic stages from raw material comprising: raw material preparation and coke making, iron making, steel making, casting and primary rolling and finishing. In the raw materials preparation step, the ores, essentially iron oxides containing some impurities, are agglomerated into particles at least roughly the size of small marbles before they are introduced into blast furnaces. These particles generally are mixtures of fine ore particles, lime stone and other material made to undergo partial fusion. The coke is made from ground coal heated in the absence of air to drive off volatile matter, moisture and sulfur. The resultant metallurgical coke is utilized as a reducing agent and as a fuel in iron making. Iron making is conducted in iron blast furnaces wherein iron ore, (sinter or pellets), a flux (lime stone) and metallurgical coke are charged at the top while preheated air is blown into the system at the bottom. Oxygen and minerals are removed from the iron ores, reducing them to metallic iron during their descent through the blast furnace. As an alternative to the blast furnace, a direct reduction process can be utilized wherein iron ore pellets are contacted within an ascending flow or reducing gas to form a solid sponge iron which is melted and refined in an electric arc furnace to obtain steel. In the steel making step, the metal obtained from the blast furnace by direct reduction is purified by selectively oxidizing impurities such as carbon, silicon, manganese, sulfur and phosphorous. In the open hearth steel making process, hot metal and scrap are heated by burning oil or natural gas in a shallow reverbatory furnace. The present preferred steel making process is the basic oxygen process in which molten iron and scrap are introduced into a pear shaped vessel and then a supersonic oxygen jet is blown into the bath surface. Another alternative involves the use of electric furnaces which can utilize the scrap and/or molten hot metal wherein an arc is struck between electrodes and the metal charge to provide the needed thermal energy to melt the charge and oxidize the impurities within an injected oxygen stream. The steel thus obtained is cast into ingots which are then further processed in primary and finishing rolling mills into the desired shape. Presently, the energy requirement for one ton of steel is about 35 million BTU.
It would be highly desirable to provide a method for making steel from iron ore which materially reduces present commercial energy requirements. More particularly, it would be highly desirable to provide such a process which eliminates the need for processing iron-containing material through the liquid state when making steel.